Sergei Skripal
Britain pointed the finger at Russian President Vladimir Putin on Thursday for a nerve agent attack on a former Russian spy in England.
Washington it would impose fresh sanctions on Russia by the end of August after it determined that Moscow had used a nerve agent against a former Russian agent.
Britain's security minister dismissed a report that police have identified several Russians who were behind the poisoning of Skripal as “wild speculation”.
Police briefly cordoned off part of the English city of Salisbury near where former Russian double agent Sergei Skripal and his daughter were found poisoned.
A British woman has died after being exposed to the nerve agent Novichok in western England, the Metropolitan Police said in a statement on Sunday.
In the southern English city of Salisbury counter-terrorism detectives stepped up their investigation into how people were exposed to the nerve agent Novichok.
Britain would consider launching a cyber attack against Russia in retaliation if Russia targeted British national infrastructure.
Yulia Skripal, who was poisoned in Britain last month along with her father, a former Russian spy.
Former Russian spy Sergei Skripal is no longer in critical condition and his health is improving rapidly more than a month since he was poisoned with a nerve agent
Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) conducted an inspection at an undisclosed location in Russia in the past week
Russia lost a bid Wednesday at the global chemical weapons watchdog to launch a joint probe with Britain into the spy poisoning scandal.
Former Russian spy Sergei Skripal and his daughter first came into contact with a nerve agent at their home address in Britain.
Russia accused Britain of trying to force its allies to take "confrontational steps" after EU member states decided to recall the bloc's envoy from Moscow.
Britain accused Russia of spreading "half-truths and half-lies" in a U.N. debate on Tuesday over a nerve toxin attack on a Russian double agent.
Czech Foreign Minister Martin Stropnicky on Saturday denied Moscow's accusation that the nerve toxin used against a former Russian double agent.
Britain on Friday provoked Russia's wrath by directly implicating Vladimir Putin in the nerve agent attack on an ex-double agent.
23 diplomats to be removed, Russian state assets frozen, high-level bilateral meetings cancelled along with diplomatic trips to the World Cup in Russia this summer.
British police have identified more than 200 witnesses and are looking at more than 240 pieces of evidence in their investigation into a nerve agent attack on a Russian ex-spy.
Britain warned it would respond "robustly" if it emerged that a government was behind the suspected poisoning of a former Russian double agent.